It is well known in the art that fresh roasted coffee gives off substantial amounts of carbon dioxide and other gases, particularly after grinding. U.S. Pat. No. 1,992,556 issued to Tone on Feb. 26, 1935 teaches that roasted coffee, after it is ground, may be quickly sealed in containers in which the air has been replaced by an inert gas. Prior to sealing, the container is placed within a chamber and air is withdrawn from the chamber to create a vacuum on the chamber and the container. The vacuum is replaced by an inert gas which is delivered into the chamber under a pressure slightly above atmospheric pressure. The chamber is again placed under vacuum and the vacuum is again replaced by admitting an inert gas into the chamber. This cycle of operations may be continued until practically all of the air has been drawn out of the container and replaced by the inert gas. The cover closing the open end of the container is thereafter double seamed onto the container. According to the teachings of Tone, the gas contained within the roasted coffee will continue to evolve in the sealed container until the pressure of the container balances the pressure in the coffee cells, thereby preventing further evolution of gas from the roasted coffee. Tone states that when the coffee is opened, the coffee is practically in the same condition of freshly ground coffee, that is, the oils are free from rancidity and the coffee gas is housed within the cells of the coffee ready to evolve and pass off from the coffee in the same way that it does from the freshly ground coffee.
Tone does not disclose either the extent to which drawing vacuum prior to sealing of the container removes gases from the coffee or the gas pressure which is ultimately reached within the sealed container prior to opening. In addition Tone fails to disclose how the pressurized coffee is controlled when the container is initially opened or what happens to the coffee which is not immediately used upon initial opening of the container.
If coffee is packaged immediately after roasting and grinding without substantial off gassing, industry experience has demonstrated that the pressure of the carbon dioxide and other gases liberated from the coffee may cause serious bulging and even rupture of substantially gas-impervious bags, canisters or other containers used in the packaging.
According to the teachings of U.S. Pat. No. 2,430,663 issued to Behrman on Nov. 11, 1947, several methods have been used to overcome the difficulties caused by the development of pressure within substantially gas-impervious packages of roast and ground coffee. In connection with the use of glass jars and tin cans, Behrman teaches that vacuum packing has been practiced. In such packing it has been customary to use oversized containers to leave space for expansion. Even so, Behrman teaches that the pressure of the liberated carbon dioxide more than compensates for the vacuum packing with the result that when a can or jar of roast and ground coffee which has been packed prior to substantial off gassing is opened, a hissing noise is heard which is due, not to incoming air, but to escaping carbon dioxide.
Behrman further teaches that the problem encountered with flexible bags and other nonrigid containers of roast and ground coffee is that when a material is utilized which is sufficiently impermeable to prevent the ingress of atmospheric oxygen and the egress of gas evolved from the roast and ground coffee in the package, the containers are usually distorted and often ruptured by the pressure of the developing carbon dioxide.
One approach to solving this problem has been to employ mechanical gas escape valves intended to relieve the build up of pressure from within the flexible container while preventing the entry of atmospheric air into the package. Representative prior art escape valves for use on flexible packages are disclosed in: U.S. Pat. Nos. 3,595,467 issued to Goglio on July 27, 1971; 3,799,427 issued to Goglio on Mar. 26, 1974; and 4,420,015 issued to Blaser on Dec. 13, 1983. However, these valves, typically increase the cost of the flexible package utilized to house the roast and ground coffee. In addition, they do not always function in their intended manner.
Still another prior art approach to the packaging of roast and ground coffee, particularly in containers comprised of substantially gas-impervious material, involves subjecting the roast and ground coffee to a holding period sufficient to allow the coffee to substantially off gas and thereafter placing it into the container using a vacuum packing operation. This typically involves holding the coffee in vented bins for some period of time, which may range from a few hours for roast and ground coffee to a few days for whole roasted coffee beans, to allow the bulk of the carbon dioxide stored in the coffee during roasting to escape. In this regard, it is generally known that gases evolve from the coffee much more rapidly once it has been ground. Accordingly, if one desires to maximize the rate of off gassing prior to packing, the coffee is preferably subjected to grinding as soon as possible after roasting.
In the case of a rigid container, such as a metal can, vacuum packing of the coffee after it has been allowed to off gas at least to a degree, usually results in a residual vacuum still being present in the can upon opening. The degree of vacuum remaining in the metal can upon opening will, however, be generally lower than that present at the time of packing due to gases evolved from the coffee contained in the package after the package has been sealed. Therefore, the more off gassing which is allowed to take place prior to packing, the greater will be the degree of residual vacuum remaining in the metal can upon opening. Unfortunately, the more off gassing which is allowed to occur, the greater will be the degree of harmful oxidation of the coffee.
In the case of substantially gas-impervious flexible containers, vacuum packing of the coffee after it has been allowed to substantially off gas causes the walls of the flexible container to collapse against the coffee, thereby producing a hard or brick-like package until the hermetic seal is broken by the consumer opening the package. Because the bulk of the carbon dioxide exits the coffee before vacuum packing, the flexible package normally retains its brick-like appearance and feel until it is opened even though the residual vacuum pressure within the bag is less at the time of opening than at the time of packing due to gases evolved from the coffee after the package has been sealed. As will be appreciated, any appreciable positive pressure developed within the flexible container by gases evolved from the coffee may cause swelling or even bursting of the container. Accordingly, flexible containers subjected to vacuum packing generally require more off gassing of the coffee prior to packing to maintain a brick-like configuration until they are opened by the consumer.
While the vacuum packed brick-like bag approach has met with reasonable success in terms of minimizing the cost of packaging materials, it increases capital and production costs, since it does require a substantial number of holding bins to allow the roast coffee to off gas prior to packaging as well as additional labor to transport the roast coffee to and from the holding bins. Unfortunately, this process does expose the roast coffee to the atmosphere during the off gassing process. As a result, some of the desirable volatile aroma and flavor containing constituents of the fresh roasted coffee may be lost or their quality may be lowered by oxidation before the coffee product is packaged.